U.S. patent application number 17/495625 was filed with the patent office on 2022-04-14 for hydrogen gas producing apparatus using photocatalyst.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is TOYODA GOSEI CO., LTD., TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Taizo MASUDA, Kenichi OKUMURA, Ryota TOMIZAWA, Atsuki YOSHIMURA.
Application Number | 20220111349 17/495625 |
Document ID | / |
Family ID | |
Filed Date | 2022-04-14 |
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United States Patent
Application |
20220111349 |
Kind Code |
A1 |
MASUDA; Taizo ; et
al. |
April 14, 2022 |
HYDROGEN GAS PRODUCING APPARATUS USING PHOTOCATALYST
Abstract
In an apparatus producing hydrogen gas by the decomposition
reaction of water using photocatalyst, its miniaturization is
achieved while suppressing the decrease of production efficiency of
hydrogen gas as low as possible or improving the efficiency. The
apparatus 1 comprises a container portion 2 receiving water W; a
photocatalyst member 3 immersed in the water, having photocatalyst
which generates excited electrons and positive holes when
irradiated with light, causes a decomposition reaction of the water
and generates hydrogen gas; a light source 4 emitting the light
irradiated to the photocatalyst member; and a heat exchange device
7 conducting waste heat of the light source to the water in the
container portion; wherein the water to be decomposed on the
photocatalyst member in the container portion is warmed by the
waste heat of the light source by the heat exchange device.
Inventors: |
MASUDA; Taizo;
(Yokohama-shi, JP) ; OKUMURA; Kenichi;
(Gotemba-shi, JP) ; TOMIZAWA; Ryota; (Toyota-shi,
JP) ; YOSHIMURA; Atsuki; (Susono-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA
TOYODA GOSEI CO., LTD. |
Toyota-shi
Kiyosu |
|
JP
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
TOYODA GOSEI CO., LTD.
Kiyosu
JP
|
Appl. No.: |
17/495625 |
Filed: |
October 6, 2021 |
International
Class: |
B01J 19/12 20060101
B01J019/12; B01J 19/00 20060101 B01J019/00; B01J 16/00 20060101
B01J016/00; C01B 3/04 20060101 C01B003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 11, 2020 |
JP |
2020-171600 |
Claims
1. A hydrogen gas producing apparatus, comprising: a container
portion which receives water, a photocatalyst member placed in the
container portion to be immersed in the water therein, which member
has photocatalyst which generates excited electrons and positive
holes when it is irradiated with light, causes a decomposition
reaction of the water which decomposes water into hydrogen and
oxygen and generates hydrogen gas; a light source emitting the
light which is irradiated to the photocatalyst member and induces
the decomposition reaction of the water; and a heat exchange device
which conducts waste heat of the light source to the water in the
container portion; wherein the water to be decomposed on the
photocatalyst member in the container portion is warmed by the
waste heat of the light source by the heat exchange device.
2. The apparatus of claim 1, wherein the light source is operated
with electric power obtained by solar power generation and emits
the light irradiated to the photocatalyst member while waste heat
in the operation of the light source is conducted to the water by
the heat exchange device.
3. The apparatus of claim 1, wherein a density of the light
irradiated to the photocatalyst member is adjusted at or lower than
a density which gives a photocatalyst efficiency more than a
predetermined value, which efficiency is a ratio of an amount of
the generated hydrogen gas per photon quantity entering into the
photocatalyst.
4. The apparatus of claim 1, wherein the apparatus is designed to
confine the light emitted from the light source in the container
portion.
5. The apparatus of claim 4, wherein the container portion has a
light reflecting mechanism for confining the light emitted from the
light source in the container portion.
6. The apparatus of claim 4, wherein the photocatalyst member is a
member on which the photocatalyst is formed in layer, and the
photocatalyst layer is formed in a thickness that not all the light
is absorbed in the photocatalyst when the light enters into the
photocatalyst layer for the first time, and the light which
penetrated through the photocatalyst member is irradiated again to
the photocatalyst member.
7. The apparatus of claim 1, wherein the container portion has a
heat insulation mechanism which suppresses heat dissipation from
the water to outside of the container portion.
8. The apparatus of claim 1, wherein the photocatalyst member
comprises plural plate members in which the photocatalyst is fixed
in layer in a surface direction of each of the plate members, the
plate members being arranged so that their respective surfaces are
mutually faced and inclined to become closer to one another as
those are farther away from the light source, and an incident angle
of the light emitted from the light source to each surface of the
plate members is larger than 0.degree..
9. The apparatus of claim 8, wherein the layer of the photocatalyst
of the photocatalyst member is formed in a thickness which
increases as it is farther away from the light source.
10. The apparatus of claim 8, wherein the photocatalyst member is
designed to satisfy a condition that the light emitted from the
light source reflects on the plate members twice or more.
11. The apparatus of claim 2, wherein a rated output of the light
source is adjusted so that a light emitting efficiency of the light
source will be maximized when a current is supplied to the light
source at a rated current value of the solar power generation.
12. The apparatus of claim 2, wherein the light source includes two
or more LEDs, and a number of operated LEDs in the two or more LEDs
is changed so that a light emitting efficiency of the light source
will be maximized in accordance with an output current of the solar
power generation.
13. The apparatus of claim 1, wherein an emission wavelength of the
light source is selected to fall in a wavelength band in which a
quantum yield of the photocatalyst exceeds beyond a predetermined
threshold value.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Japanese Patent
Application No. 2020-171600 filed on Oct. 11, 2020, which is
incorporated herein by reference in its entirety including the
specification, drawings, and abstract.
TECHNICAL FIELD
[0002] This invention relates to a hydrogen gas producing
apparatus, and more specifically to a device which produces
hydrogen gas by the decomposition reaction of water using
photocatalyst.
BACKGROUND ART
[0003] Hydrogen gas is expected to be used as a next generation
clean fuel which does not produce carbon dioxide. Since the
hydrogen gas can be produced by the decomposition reaction of water
by light energy with photocatalyst, there have been proposed
various techniques of producing hydrogen gas using photocatalyst.
For instance, JPH9-510657 and JP2003-251197 disclose a
photocatalyst which induces the decomposition reaction of water by
irradiation of ultraviolet light or visible light to produce
hydrogen gas and its preparation method. JP2013-234077 discloses a
structure of a hydrogen production device comprising an oxidation
reaction means of water by light, from ultraviolet to visible, in
the sunlight using photocatalyst, and a reduction reaction means of
water using the heat of light, from infrared to visible, in the
sunlight. JP2015-218103 proposes a structure of a hydrogen
producing apparatus wherein water into which photocatalyst
particles are dispersed is circulated in a housing having a light
receiving window so that the decomposition reaction of water by
light, producing hydrogen gas will occur. JP2017-24956 proposes a
structure of a hydrogen generation system in which, by irradiating
light accumulated by a sunlight condenser to a receiver including
an electrode consisting of photocatalyst placed in water, charged
particles in the photocatalyst are excited so that water around
them will be electrolyzed, producing hydrogen gas continuously. In
this regard, in JP2016-108181, though not a technique of producing
hydrogen gas, there has been disclosed a technique that a carbon
plate material of carbon allotrope of sp3 crystal structure is
immersed in a solvent in which carbon dioxide is dissolved, and by
irradiating the solvent with ultraviolet light while raising the
temperature of the solvent by a heater, the carbon material is
excited such that C.dbd.O bonds in the carbon dioxide are
separated, generating methane with carbon monoxide generation.
SUMMARY
[0004] In techniques of producing hydrogen gas by irradiating light
to photocatalyst immersed in water to cause the decomposition
reaction of water as described above, it is advantageous that the
size of an apparatus or a system can be made as small as possible.
As one way for this, it is considered to increase the amount of
hydrogen gas produced in photocatalyst per unit quantity by
increasing the density of light (light intensity) irradiated on the
photocatalyst per unit quantity so as to increase the densities of
excited electrons and positive holes generated in the
photocatalyst. For instance, in a case that the solar energy, which
is one of renewable energies, is used for the production of
hydrogen gas, if photocatalyst is irradiated with the sunlight as
it is, its light density is comparatively low so that it would be
required to make the space occupied by the photocatalyst large in
order to supply a large amount of light energy to the
photocatalyst, and thus, by raising higher the density of light
irradiated to the photocatalyst, it will become possible to make
the space occupied by the photocatalyst smaller and thereby make
the size of the system or device for the production of hydrogen
more compacted. In this respect, however, according to the research
by the inventors of this invention, as explained in detail in the
column of embodiments later, surprisingly, it was found that, when
the light density irradiated to photocatalyst was increased, the
production efficiency of hydrogen gas (the produced amount of
hydrogen gas per incident light amount) decreased. This is
considered because, even if the densities of excited electrons and
positive holes generated in the photocatalyst are increased by the
increase of light intensity, the speed of the decomposition
reaction of excited electrons, positive holes and water molecules
is so slow that an excited electron and a positive hole will
recombine to one another before reacting with a water molecule,
respectively, and thereby the light energy is not effectively used
for the production of hydrogen gas. From this fact, it has been
revealed that, when the density of the light irradiated to
photocatalyst is simply increased for making a hydrogen production
system or device compacted, the production efficiency of hydrogen
gas per the irradiated light amount decreases and thus the
miniaturization and the efficiency increasing of the apparatus
would be incompatible with one another.
[0005] By the way, in the further research of the inventors of this
invention, it was also found out that the production efficiency of
hydrogen gas increased with the increase of the temperature of
water which is the reactant. Thus, in the miniaturization of the
hydrogen gas producing apparatus or system, it is considered that
the decrease of the efficiency of the hydrogen gas production due
to the increase of the density of the light irradiated on
photocatalyst can be compensated by raising the water temperature.
In that case, if the waste heat of a light source which generates
the light irradiated to the photocatalyst can be used for warming
the water instead of using a different heater which supplies energy
from the outside, more concretely, if, in addition to the radiant
heat from the light source to the water, the light source is
equipped with a heat exchange device which directly conducts the
waste heat to the water so that it can be warmed sufficiently for
raising the production efficiency of hydrogen gas, it becomes
possible to improve more the utilization efficiency of the energy
in connection with the hydrogen gas production. This knowledge is
used in the present embodiment.
[0006] Thus, the main object of the present embodiment is to
provide an apparatus which produces hydrogen gas by the
decomposition reaction of water using photocatalyst, having a
structure which can achieve the miniaturization of the apparatus
while suppressing the reduction of the production efficiency of
hydrogen gas as low as possible or while improving the production
efficiency of hydrogen gas.
[0007] Moreover, another object of the present embodiment is to
provide an apparatus as described above, which is so constructed
that the utilization efficiency of the energy in connection with
hydrogen gas production can be more improved.
[0008] According to one manner of the present embodiment, the
above-mentioned object is achieved by a hydrogen gas producing
apparatus, comprising: [0009] a container portion which receives
water, [0010] a photocatalyst member placed in the container
portion to be immersed in the water therein, which member has
photocatalyst which generates excited electrons and positive holes
when it is irradiated with light, causes a decomposition reaction
of the water which decomposes water into hydrogen and oxygen and
produces hydrogen gas; [0011] a light source emitting the light
which is irradiated to the photocatalyst member and induces the
decomposition reaction of the water; and [0012] a heat exchange
device which conducts waste heat of the light source to the water
in the container portion; [0013] wherein the water to be decomposed
on the photocatalyst member in the container portion is warmed by
the waste heat of the light source by the heat exchange device.
[0014] In the above-mentioned structure, as noted above, a
"photocatalyst" may be a substance which can cause the
decomposition reaction of water when it is irradiated with light,
and reduce water to generate hydrogen gas. The "photocatalyst
member" may be a member formed of the photocatalyst material itself
or a member formed by fixing the photocatalyst material on an
arbitrary board or substrate. Typically, the "light source" may be
of arbitrary type, which receives supply of electric power and
emits the light to be absorbed into the photocatalyst and induce
the decomposition reaction of water. Further, in order that the
light irradiated to the photocatalyst may efficiently be absorbed
into the photocatalyst and generate excited electrons and positive
holes, the emission wavelength of the light source is preferably
chosen to fall into a wavelength band in which the quantum yield of
the photocatalyst exceeds a predetermined threshold value (which
may be chosen arbitrarily). In this respect, as illustrated in the
column of the embodiment later, the quantum yield of a typical
photocatalyst increases rapidly when the wavelength of irradiated
light becomes lower than near a certain wavelength. Accordingly,
the light source may be chosen so that the emission wavelength of
the light source will be in the shorter wavelength side than the
wavelength at which the rapid increase of the quantum yield of the
photocatalyst occurs. For the photocatalyst to be used in the
present embodiment, for example, SrTiO.sub.3 (strontium titanate),
Ga.sub.2O.sub.3 (gallium oxide), GaN (gallium nitride), NaTaO.sub.3
(sodium tantalate), TiO.sub.2 (titanium oxide), etc. can be used.
On the other hand, for the light source, various light emission
diodes (LED) may be employed, and concretely, light sources using
indium gallium nitride (InGaN), diamond (ultraviolet), gallium
nitride (GaN)/aluminum gallium nitride (AlGaN) (ultraviolet, blue),
zinc selenide (blue), or zinc oxide (near-ultraviolet, purple,
blue) can be used. Then, in the structure of the present apparatus,
as described above, the "heat exchange device" is provided. For the
heat exchange device, an arbitrary form may be employed as long as
the waste heat of the light source can be conducted to the water in
the container portion. In one manner, as illustrated in the column
of the embodiment later, the light source may be provided with a
structure which achieves the function of a heat exchanger
conducting the waste heat discharged from the light source to
liquid, and in that structure of the heat exchanger, there may be
installed a structure of circulating the water in the container
portion. Moreover, alternatively, the light source, waterproofed,
may be contacted to or immersed in the water in the container
portion so that the waste heat of the light source may be conducted
to the water.
[0015] In the structure of the above-mentioned present embodiment,
in the apparatus that produces hydrogen gas by irradiating light to
photocatalyst in contact with water to cause the decomposition
reaction of water, there is provided a structure which warms the
water by the waste heat of the light source. According to this
structure, in a case of miniaturizing the hydrogen gas producing
apparatus by increasing the density of the light irradiated to the
photocatalyst per unit quantity to decrease the space which
photocatalyst occupies, the decrease in the production efficiency
of hydrogen gas due to the increasing of the density of the light
irradiated to the photocatalyst can be compensated by warming the
water which is the reactant. In this structure, moreover, because
the warming of the water is achieved using the waste heat of the
light source, there is no need to separately prepare a heater, etc.
for warming the water, and thus, it is not necessary to supply
energy separately for warming the water, so that the improvement in
the efficiency of energy required for production of hydrogen gas
will be attained. Namely, in accordance with the structure of the
above-mentioned present apparatus, the apparatus can be
miniaturized while the decrease in the efficiency of hydrogen gas
production can be suppressed, and also, the improvement of the
energy efficiency can be achieved. In this regard, as explained
also in the column of the embodiment later, since the photocatalyst
efficiency indicating the efficiency of hydrogen gas production
(the ratio of the amount of production of hydrogen gas per photon
quantity which enters into the photocatalyst) increases as the
density of the irradiated light (irradiated light intensity)
becomes lower, in order to achieve a desired photocatalyst
efficiency, the density of the light irradiated to the
photocatalyst member may be adjusted to be at or lower than a
density which gives the photocatalyst efficiency at more than a
predetermined value which may be chosen arbitrarily. Here, what is
important is that, in the present apparatus, since the
photocatalyst efficiency is raised by warming the water, it is
possible to increase the density of the irradiated light for
achieving a certain efficiency of hydrogen gas production, and
corresponding to this, the miniaturization of the apparatus can be
achieved without dropping the efficiency of hydrogen gas
production.
[0016] In the structure of the above-mentioned present apparatus,
since the temperature of the water in the container portion is
higher than the surrounding normal temperature owing to its
warming, heat dissipation from the water in the container portion
to the outside of the container portion easily occurs without
anything to cover it. Then, in order to prevent the heat
dissipation from the warmed water, suppress the decrease in the
photocatalyst efficiency and make the waste heat of the light
source used more effectively, the container portion may have a heat
insulation mechanism for suppressing the heat dissipation from the
water to the outside of the container portion. For instance, a heat
insulation structure may be provided by making the container
portion of material with high insulation efficiency or covering the
container portion with thermal insulation material.
[0017] Further, in the structure of the above-mentioned present
apparatus, in order to make the light emitted from the light source
be effectively absorbed into the photocatalyst and contribute to
the decomposition reaction of water, it is preferable that the
apparatus is designed so that the light emitted from the light
source will be confined in the container portion. For this, in one
manner, the container portion may have a light reflecting mechanism
for confining the light emitted from the light source in the
container portion. For instance, the light reflecting mechanism is
formed by covering the inside of the container portion with
reflective mirrors or by placing a reflective mirror adjacent the
photocatalyst member.
[0018] Furthermore, in the structure of the above-mentioned present
apparatus, the photocatalyst member may be a member in which
photocatalyst is made in a layered form such that the photocatalyst
layer is formed to have a thickness at which not all the light is
absorbed in the photocatalyst when the light enters into the
photocatalyst layer for the first time, and thereby the light which
has penetrated the photocatalyst member once will be irradiated to
the photocatalyst member again, owing that the light is confined in
the container portion. In the photocatalyst, in order that the
excited electrons generated by the irradiated light as much as
possible can reduce the hydrogen atoms of water to contribute to
the generating of hydrogen gas before the recombination to positive
holes, it is preferable that the water can reach easily to the
photocatalyst which absorbed light. Thus, as noted above, in the
case that the photocatalyst layer is formed to have a thickness at
which not all the light is absorbed in the photocatalyst when the
light enters into the photocatalyst layer for the first time, the
amount of the light absorbed in a region in the photocatalyst
layer, distant from its surface, to which the water cannot easily
reach in the photocatalyst, is decreased, and on the other hand,
the light which has penetrated the photocatalyst member without
being absorbed therein is irradiated to the photocatalyst member
again because of the structure of confining the light in the
container portion, and then absorbed in the photocatalyst to
generate excited electrons so that it will contribute to generating
hydrogen gas, and therefore, after all, the much more light can be
absorbed into the photocatalyst in its region near its surface
where the water reaches easily, contributing the generation of
hydrogen gas, and accordingly, it is expected that the more amount
of hydrogen gas can be produced.
[0019] In the above-mentioned present apparatus, concretely, the
photocatalyst member may be a plate member on which photocatalyst
is fixed in a layer form in the surface direction. Then, in one
manner, the photocatalyst member may be constructed by arranging
plural plate members as above to be inclined such that their
surfaces are mutually faced while being closer to each other as
those are away from the light source, and it is preferable that the
incident angle of the light emitted from the light source to the
respective surfaces of the plate members is larger than 0.degree..
According to this structure, after the light emitted from the light
source strikes upon one in the plural members, the light which
reflected from that will strike upon the opposite member, and
thereby it becomes possible to make the more amount of the light be
absorbed into the photocatalyst and contribute to the generation of
hydrogen gas. In this regard, the reason that the incident angle of
the light is made larger than 0.degree. is to prevent the
reflecting ray of the light from returning toward the light source
without hitting on any other faced members. Further, in the
structure that the light advances between the plurality of mutually
faced plate members while reflecting thereon as noted above, since
the number of times of reflection of the light increases and the
density of the light becomes higher as the regions of the members
are farther from the light source, the photocatalyst layers of the
photocatalyst plate members may be formed such that, as the region
of the layer is farther from the light source, their thicknesses
increase, and thereby, in the photocatalyst member, together with
the increasing of the absorbed amount of the light by the
photocatalyst, the amount of the photocatalyst may be adjusted
corresponding to the density of the light in order for the
photocatalyst amount to be distributed efficiently (the
optimization of the photocatalyst amount). In this connection, the
photocatalyst member in which plural plate members as described
above are arranged may be designed so as to satisfy a condition
that the light emitted from the light source reflects on the plate
member twice or more.
[0020] In the above-mentioned present apparatus, the light source
may be designed to be operated with electric power obtained by
solar power generation to emit the light irradiated to the
photocatalyst member while the waste heat during its operation is
conducted to the water by the heat exchange device. According to
this, the production of hydrogen gas will be achieved by renewable
energy. Further, in accordance with the operating of the light
source with the electric power obtained from the sunlight instead
of the irradiating of the sunlight itself to the photocatalyst
member, it becomes possible to supply light energy to the
photocatalyst member while condensing the low solar energy per unit
area, achieving the miniaturization of the apparatus.
[0021] By the way, when the light source is operated with electric
power, it is preferable that the light emission efficiency of the
light source is maximized. Thus, in a case that the light source is
operated with the electric power obtained by the solar power
generation, the rated output of the light source may be adjusted so
that the light emission efficiency of the light source will be
maximized when current is supplied to the light source at the rated
current value of the solar power generation. Thereby, the solar
energy can be more effectively used for the production of hydrogen
gas. Furthermore, in the case of the solar power generation, its
output is changed by the sunshine condition, and the available
current is changeable every moment. In that case, the efficiency of
the energy used in the production of hydrogen gas becomes better
when the light source is operated at every moment so that its light
emission efficiency will be maximized. In this respect, plural LEDs
may be employed for the light source, and in that case, since the
light emission efficiency of each LED changes according to the
current supplied thereto, the light source may be designed such
that the number of LEDs being operated in the plural LEDs is
changed in accordance with the output current of the solar power
generation in order to maximize the light emission efficiency of
the light source. Then, it is expected that solar energy can be
more effectively converted into the light from the light source and
used for production of hydrogen gas.
[0022] Thus, according to the above-mentioned present embodiment,
in the technique of producing hydrogen gas by the decomposition
reaction of water using photocatalyst, based upon the knowledge
that, although the photocatalyst efficiency would decrease when the
density of the irradiated light becomes higher, the decrease in the
photocatalyst efficiency can be compensated by raising the
temperature of water which is the reactant, a hydrogen gas
producing apparatus using photocatalyst is equipped with a heat
exchange device which warms the water by the waste heat of a light
source, and thereby, the decrease in the photocatalyst efficiency
due to the increase of the density of the irradiated light is
compensated through the warming of the water with the waste heat of
the light source, and accordingly, there is provided a structure
enabling the achievement of the miniaturization of the apparatus
while suppressing the decrease in the efficiency of hydrogen gas
production as low as possible together with attaining the increase
in the energy efficiency. Furthermore, especially, according to the
structure of warming water by the waste heat of the light source,
the water temperature can be surely raised rather than in a case
where the water is warmed solely by the radiant heat of the light
source, and thereby the suppression of the decrease in the
photocatalyst efficiency is more expected. Also, in the case of the
manner in which the light source of the present apparatus is
operated with electric power of the solar energy origin, it becomes
possible to obtain hydrogen energy efficiently without emitting
carbon dioxide.
[0023] Other purposes and advantages of the present embodiments
will become clear by explanations of the following preferable
embodiments.
BRIEF DESCRIPTIONS OF DRAWINGS
[0024] FIG. 1 is a schematic drawing of one embodiment of a
hydrogen gas producing apparatus according to the present
embodiment.
[0025] FIG. 2 is a drawing showing the examples of the wavelength
characteristics of absorptivity and quantum yield of a typical
photocatalyst (SrTiO.sub.3) and the emission wavelength
characteristic of a light source (InGaN series LED), used for the
hydrogen gas producing apparatus according to the present
embodiment. The data were measured by the inventors of the present
embodiment.
[0026] FIG. 3A is a graph chart showing the change of the
photocatalyst efficiency against the density of the light (light
intensity) irradiated to photocatalyst.
[0027] FIG. 3B is a graph chart showing the change of the
photocatalyst efficiency against the temperature in water contacted
to photocatalyst, obtained through experiments. The data were
measured by the inventors of the present embodiment.
[0028] FIG. 4 is a schematic drawing of another embodiment of the
hydrogen gas producing apparatus according to the present
embodiment.
[0029] FIG. 5A is a schematic drawing of a photocatalyst layer of a
photocatalyst member in the hydrogen gas producing apparatus
according to the present embodiment, showing a situation that
irradiated light which penetrates a photocatalyst layer once is
reflected by a reflector and irradiated again to the photocatalyst
layer. FIG. 5B is a schematic drawing of another embodiment of the
hydrogen gas producing apparatus according to the present
embodiment, showing an example that plural photocatalyst members
are arranged in a V-shape form. FIG. 5C is a drawing explaining the
relation between the directional angle .theta. of the range of the
rays of the light emitted from the light source in FIG. 5A, and the
included angle .psi. of the photocatalyst members arranged in the
V-shape form. FIG. 5D is a schematic drawing of the embodiment
where more advantageous characteristic structure is added to the
structure of FIG. 5A.
[0030] FIG. 6 is graph charts of the change of the raising rates of
the water temperature to itself in the structure of warming water
with the waste heat of a light source by a heat exchange device as
shown in FIGS. 1, 5A, and 5C, obtained by the simulation, wherein
the cases where the container portion is equipped with the heat
insulation mechanism and without it are shown. The data were
obtained through simulations by the inventors of the present
embodiment.
[0031] FIG. 7A is a graph chart showing the change of the light
emission efficiency of a light source against the current supplied
thereto, where the light source was formed by four LEDs being
connected in parallel to an electric source, obtained by
experiment. FIG. 7B is a graph chart showing the change of the
light emission efficiency of a light source to the current supplied
thereto, where the light source was formed by one LED being
connected to an electric source. The data were obtained through
experiments by the inventors of the present embodiment.
[0032] FIG. 8A-8C are drawings showing schematically circuit
configurations of a light source in which the number of LEDs
operated in accordance with the amount of generated current of a
solar panel.
DETAILED DESCRIPTIONS OF EMBODIMENTS
[0033] Basic Structure of Hydrogen Gas Producing Apparatus
[0034] Referring to FIG. 1, the hydrogen gas producing apparatus 1
of this embodiment, in its basic structure, has a container portion
2, having an arbitrary form, which receives water (liquid) W; a
photocatalyst member 3 which carries photocatalyst and is contacted
to or immersed in the water W in the container portion 2; a light
source device 4 which emits light to be irradiated to the
photocatalyst member 3; a heat exchange device 7 for warming the
water W stored in the container portion 2 by the waste heat of the
light source device 4; and a gas pipe 8 which sends generated
hydrogen gas and oxygen gas to a separator.
[0035] In the structure of this hydrogen gas producing apparatus 1,
the photocatalyst member 3 is a member carrying photocatalyst
material which, when irradiated with light, can absorb photons,
generate excited electrons and positive holes, cause the
decomposition reaction of water where the water is reduced, and
generate hydrogen gas, and the member may be formed of the
photocatalyst material itself, or be prepared by fixing
photocatalyst material on an arbitrary board or substrate. The
photocatalyst member 3 may be typically formed in a plate form as
illustrated, but not limited thereto if the photocatalyst material
can contact to the water W. For instance, in one manner, the
photocatalyst member 3 may be formed by placing the powder of a
photocatalyst material over a glass substrate or a ceramic board,
and heating and sintering it. Or, a substrate formed by hardening
photocatalyst material in a plate form may be employed as the
photocatalyst member 3. For the photocatalyst material used in this
embodiment, as noted above, any material which can generate
hydrogen gas from water through the irradiation of light, used in
this field, may be used, and concretely, for example, SrTiO.sub.3
(strontium titanate), Ga.sub.2O.sub.3 (gallium oxide), GaN (gallium
nitride), NaTaO.sub.3 (sodium tantalate), TiO.sub.2 (titanium
oxide), etc. can be used. As shown in FIG. 2, the photocatalyst
material typically exhibits a wavelength characteristic that, when
the wavelength of the irradiated light is changed shorter from a
long wavelength, its absorptivity and quantum yield increase
rapidly near a certain wavelength (The generated amounts of excited
electrons and positive holes because of the absorption of photons
increase in the wavelength band in which the absorptivity and
quantum yield increase.).
[0036] The light source device 4 may be an arbitrary light source
which emits the light of a wavelength which is absorbed by the
photocatalyst material on the above-mentioned photocatalyst member
3 to generate excited electrons and positive holes. In this
respect, more in detail, as in FIG. 2 noted above, the absorptivity
and quantum yield of the photocatalyst material have wavelength
characteristics which increase when the light in the wavelength
band shorter than a certain wavelength is irradiated, and
therefore, for the light source device 4, a light emitting element
or a light-emitting object which generates the light in the
wavelength band where the absorptivity and quantum yield of the
photocatalyst material of the photocatalyst member 3 increase is
chosen preferably. Concretely, for the light emitting element or
light-emitting object of the light source, various light emission
diodes (LED) using indium gallium nitride (InGaN), diamond
(ultraviolet), gallium nitride (GaN)/aluminum gallium nitride
(AlGaN) (ultraviolet, blue), zinc selenide (blue), zinc oxide
(near-ultraviolet, purple, blue), etc. may be employed. For
instance, in a case that SrTiO.sub.3 is used as photocatalyst
material of FIG. 2, since its absorptivity and quantum yield will
increase when the wavelength of the irradiated light is less than
380 nm, an LED of InGaN series which has a peak of an emission
wavelength in 360-370 nm can advantageously be used for the
light-emitting object of the light source device 4.
[0037] Then, in the hydrogen gas producing apparatus 1 of this
embodiment, the heat exchange device 7 for warming the water W in
contact with the photocatalyst member 3 in the container portion 2
with the waste heat of the light source device 4 as noted above is
provided, and thereby, both the miniaturization of the apparatus
and improvement of the efficiency of hydrogen gas production are
achieved while suppressing the loss of energy as low as
possible.
[0038] In this respect as noted in the column of "SUMMARY",
according to research of the inventors of the present embodiment,
it has been found out through the experiment described below that
the efficiency of the hydrogen gas production by photocatalyst
decreases when the density of the light (light intensity)
irradiated to the photocatalyst is increased while the same
efficiency raises when the temperature of the water which is the
reactant is raised.
[0039] In the experiment, a photocatalyst member prepared by
spreading and sintering 100 mg SrTiO.sub.3 (strontium titanate) on
a glass plate was immersed in 200 ml of water put in a container
made of silica glass, and then irradiated with 365 nm light at
various light intensities by LED (maximum output 0.691 W) of a spot
type while adjusting water temperature to various values with a
heater, and thereby, hydrogen gas generated by the induced
decomposition reaction of water was collected, and the amount of
the gas was measured. The irradiated area of the light was 2
cm.sup.2. The output of the LED (the irradiated light intensity)
was adjusted while measuring it with a power meter (Ophir Japan
50(150)A-BB26). The amount of the irradiated light to the
photocatalyst (incident light amount) was computed by the
following:
Incident light amount
(mmolcm.sup.-2hr.sup.-1)=P.times..lamda..times.3600/(Ahc)
Here, P is an LED output (Wcm.sup.-2); .lamda., wavelength=365
(nm); A, Avogadro's number (mol.sup.-1); h, Planck constant (Js);
and c, the velocity of light (ms.sup.-1). And, the efficiency of
hydrogen gas production (photocatalyst efficiency) was computed by
the following;
Photocatalyst efficiency (%)=[Generated amount of hydrogen gas
H.sub.2.times.2]/[Incident light amount]
Here, the unit of the generated amount of hydrogen gas is
mmolcm.sup.-2hr.sup.-1 (The amount of reduction of hydrogen ions is
twice of the hydrogen gas.).
[0040] In the results, first, referring to FIG. 3A, when the LED
output was changed to be at 5%, 10%, 20%, 60%, and 100% of its
maximum output under the condition of the water temperature of
25.degree. C. (room temperature), the photocatalyst efficiency fell
with the increase of the LED output, i.e., the density of the
irradiated light. This is considered because, even if the densities
of excited electrons and positive holes generated in the
photocatalyst are increased by the increase of the light intensity,
the speed of the decomposition reaction of water with the excited
electrons and positive holes is slow, and thus, the excited
electrons and positive holes disappear by their recombination
before these react to water, respectively. That is, it shows that
the ratio of photon energy which contributes to the generating of
hydrogen gas decreases when the density of the light irradiated to
the photocatalyst is increased. On the other hand, referring to
FIG. 3B, when the water temperature was raised to 30.degree. C.,
40.degree. C., 50.degree. C., and 60.degree. C. while maintaining
the LED output at its maximum output, the photocatalyst efficiency
increased with the rise of the water temperature. This is
considered because the speed of the reaction of the electrons and
water by the photocatalyst is increased by the heating.
[0041] Thus, considering the results in FIGS. 3A and 3B together,
it has been shown for the hydrogen gas producing apparatus that, in
a case that the density of the light irradiated to photocatalyst is
increased so that the space occupied by the photocatalyst will be
made smaller for miniaturizing the apparatus, if the water
temperature is a normal temperature, the efficiency of hydrogen gas
production, namely, the produced amount of hydrogen gas per photon
energy supplied decreases and thus the energy efficiency decreases,
and on the other hand, if the temperature of the water, which is
the reactant, is raised, it is expected that the decrease in the
efficiency of the hydrogen gas production due to the increase in
the irradiated light density can be compensated or the efficiency
can be maintained. Moreover, with respect to the warming of water,
normally, a light source device emitting the light irradiated to
photocatalyst discharges waste heat with the light, and if the
waste heat of the light source device can be used for the warming
of water, it becomes unnecessary to prepare a separate heater so
that no energy will be needed to be supplied to a heater, and thus,
the saving of energy for hydrogen gas production is attained. From
the above knowledge, a heat exchange device 7 as described above is
installed in the hydrogen gas producing apparatus 1.
[0042] The heat exchange device 7 may be realized in an arbitrary
from as long as it can achieve the warming of water in the
container portion 2 with the waste heat of the light source device
4. In one manner, as schematically drawn in FIG. 1, a heat
exchanger 7a is installed adjacent the light source device 4, and
then, the water may be warmed by pressure-feeding and circulating
the water in the container portion 2 through a water pipe 7b to the
heat exchanger 7 with a pump 7c. Furthermore, in another manner, as
schematically drawn in FIG. 4, the light source device 4 equipped
with the heat exchanger 7 and waterproofed is immersed in the water
W in the container portion 2, and thereby, the water W may be
warmed with the waste heat of the light source device 4. In that
case, for example, a stirrer 7e for generating the convection in
the water W in the container portion 2 may be provided. Or, the
light source device 4 may be placed on the bottom of the container
portion 2 while the photocatalyst member 3 may be placed on the
upper part of the container portion 2, and thereby, the water
warmed by the light source device 4 rises up toward the upper part
of the container portion 2. According to those structures using a
heat exchanger, it is advantageous in that the warming of water is
achieved more promptly than the case that only the radiant heat
from a light source is used (It is advantageous in that the warming
of water is achieved promptly also when the electric power supplied
to the light source device 4 is changed (such as when the electric
power is sent from the power production source with renewable
energy).).
[0043] In the above-mentioned structure, the density of the light
(light intensity) irradiated on the photocatalyst member 3 may be
chosen so that the photocatalyst efficiency may become
comparatively high, as shown in FIG. 3A. For instance, when an area
which receives the light irradiated to the photocatalyst member 3
is A cm.sup.2, the optical power P.sub.L(W) from the light source
device 4 may be adjusted to be 0.1.times.A (W) so that the light
intensity will be at or below 0.1 W/cm.sup.2, giving a high
photocatalyst efficiency. What should be understood is that the
decrease in the photocatalyst efficiency due to the raising of the
light intensity can be compensated by the rise of the water
temperature.
[0044] The light source device 4 of the apparatus 1 of the
above-mentioned this embodiment operates with electric power, which
may be preferably given from the energy of the sunlight origin,
generated by a solar panel, or other renewable energy. For that,
the light source device 4 may be designed so as to receive the
supply of electric power from a power production source with
renewable energy, such as a solar panel 5, through a power line
6.
[0045] In the operation of the hydrogen gas producing apparatus 1
of the present embodiment, the light source device 4 is supplied
with electric power from the power production source of a solar
panel 5, etc., and emits light, and the light is irradiated to the
photocatalyst material on the photocatalyst member 3 in the
container portion 2. Further, the water W in the container portion
2 is warmed by the heat exchange device 7 with the waste heat of
the light source device 4. Then, in the photocatalyst material, the
light is absorbed and excited electrons and positive holes are
generated, and, by the excited electrons, hydrogen of the water is
reduced to form hydrogen gas while, by the positive holes, oxygen
of the water is oxidized to form oxygen gas. After that, the
generated hydrogen gas and oxygen gas pass through the gas pipe 8,
and are sent to a separating equipment (not shown), where the
hydrogen gas is separated and collected. The separating equipment
may be an arbitrary separating equipment, using, for instance,
hydrogen separating membrane used in this field.
[0046] Improvement of Structure of Hydrogen Gas Producing
Apparatus
[0047] The structure of the hydrogen gas producing apparatus of
this embodiment may be variously improved so that the light and
waste heat, emitted from the light source device 4, may contribute
to the production of hydrogen gas more effectively, as illustrated
below.
[0048] (a) Structure Improving the Utilization Efficiency of the
Light from the Light Source Device 4
[0049] In order to make it possible to use the light from the light
source device 4 more effectively in the production of hydrogen gas,
in one manner, there may be provided a structure for confining the
light L from the light source device 4 in the container portion 2.
For instance, a light reflecting mechanism, such as a reflective
mirror, may be prepared adjacent an inner wall of the container
portion 2 or the photocatalyst member 3. In that case, the light,
which hits upon the inner wall of the container portion 2 directly
from the light source device 4 is expected to reflect there and
enter into the photocatalyst member 3. Also, as schematically drawn
in FIG. 5A, it may be designed that a part of the light L
irradiated to the photocatalyst member 3, penetrating through the
photocatalyst member 3, is reflected by the reflective mirror 9 and
the reflected light Lr enters into the photocatalyst member 3
again. In this respect, in order to cause the decomposition
reaction of water, the excited electron generated by the light
irradiated on the photocatalyst member 3 is needed to contact a
water molecule on the surface of the photocatalyst member 3
(excited electrons generated in the depth of the photocatalyst
member 3 recombines with positive holes without reacting to water
molecules.). Thus, it is preferable that the entering photons as
much as possible are absorbed on the surface of the photocatalyst
member 3. Then, in this embodiment, in a case that the
photocatalyst member 3 is a member in which photocatalyst material
is formed in a layer structure, it is preferable that the
photocatalyst layer is formed at a thickness at which not all the
light is absorbed in the photocatalyst when it enters the
photocatalyst layer for the first time. In this case, as in FIG.
5A, the light L which has penetrated through the photocatalyst
member 3 and reflected on the reflective mirror 9 will be
irradiated on the surface on the back side of the photocatalyst
member 3, and thereby, more photons are absorbed on or near the
surface of the photocatalyst member 3 (The number of photons
absorbed in the depths of the photocatalyst member 3 decreases.) so
that it becomes possible to make much more photon energy contribute
to the generating of hydrogen gas.
[0050] Moreover, in the hydrogen gas producing apparatus 1 of this
embodiment, as schematically drawn in FIG. 5B, the photocatalyst
member 3 may be formed in a structure that two or more plate
members 3a and 3b are arranged to form a V-shape such that the
respective surfaces of the plate members are mutually faced and
become closer as they are away from the light source. According to
this structure, in the light L irradiated on one of the plate
members 3a and 3b, a part of the light, reflected without being
absorbed by the photocatalyst material, is irradiated on the other
of the plate members 3a and 3b and thus, there is the opportunity
that the reflected light can be absorbed in the photocatalyst
material, and thereby, it becomes possible to make much more photon
energy contribute to the generating of hydrogen gas. In that case,
it is preferable that, in order for the light L emitted from the
light source device 4 and reflected on one of the plate members 3a
and 3b to go to the other of the plate members 3a and 3b instead of
returning toward the light source device 4, the incident angle
(.alpha.) of the light L emitted from the light source device 4 to
each surface of the plate members 3a and 3b is larger than
0.degree. (refer to FIG. 5A). In this regard, with reference to
FIG. 5C, as noted above, in a structure that the plural
photocatalyst members 3a and 3b are arranged in the V-shape form at
the included angle .psi., when the plate length x of the
photocatalyst members 3a and 3b and the distance y from the point
of the included angle of the members formed in the V-shape to the
light source device 4 satisfies x.ltoreq.ysin (.psi./2), if the ray
of the light L emitted from the light source device 4 at a
directional angle .theta. reaches one of the photocatalyst members
3a and 3b and the ray of the light Lr, reflected thereon, reaches
also the other of the photocatalyst members 3a and 3b, the
condition of .PHI.1.ltoreq..PHI.2 is fulfilled between the angle
.PHI.1=.theta./2+.psi./2, defined by the ray of the light L and one
surface of the photocatalyst members 3a and 3b, and the angle
.PHI.2=180.degree.-(.theta./2+3/2.psi.), defined by the ray of the
reflected light Lr and the other surface of the photocatalyst
members 3a and 3b. Therefore, the included angle .psi. of the
plural photocatalyst members 3a and 3b, and the directional angle
.theta. of the light source device 4 may be adjusted to satisfy the
condition:
.psi..ltoreq.90.degree.-.theta./2.
[0051] Moreover, in order for the light having penetrated through
the plural plate members 3a and 3b to enter into the plate members
3a and 3b again, there may be provided reflective mirrors 9a and 9b
on the respective sides of the plural plate members 3a and 3b
opposite to the light source device 4.
[0052] Furthermore, as noted above, in the case that the
photocatalyst member 3 is formed by the plural plate members 3a and
3b arranged in a V-shape, as schematically drawn in FIG. 5D, the
layer of the photocatalyst of the photocatalyst members 3a and 3b
may be formed such that its thickness (t1, t2) is increased as it
is farther away from the light source device 4 (t1<t2). As
illustrated, in a structure that the rays of the light (L1-L4) from
the light source device 4 advance while being reflected between the
photocatalyst members 3a and 3b arranged in the V-shape, the amount
of the reaching light increases and the density of light becomes
higher as their positions are farther away from the light source
device 4. Thus, as noted above, the thickness (t1, t2) of the
photocatalyst layer may be increased and the amount of the
photocatalyst material may be increased as it is farther away from
the light source device 4, so that the absorbed amount of the light
by the photocatalyst material will be increased. Thereby, in the
photocatalyst member 3, the amount of photocatalyst is lessened in
a place where the light intensity is low while the amount of
photocatalyst is increased in a place where the light intensity is
high, and thereby it can be avoided to use the photocatalyst
material in vain, and it can be achieved to efficiently distribute
the amount of photocatalyst.
[0053] Thus, in accordance with the above-mentioned series of
structures, the light emitted from the light source device 4 will
be absorbed much more by the photocatalyst material, while the loss
of energy supplied in the form of the light from the light source
device 4 will be suppressed.
[0054] (b) Structure Suppressing the Loss of Waste Heat from the
Light Source Device
[0055] As noted, in the hydrogen gas producing apparatus 1 of this
embodiment, the water, which is the reactant, is warmed with the
waste heat of the light source device 4. In this structure, when
the apparatus 1 is installed under a normal temperature (room
temperature), heat is radiated from the container portion 2 while
the temperature of the warmed water falls, and thereby, the energy
obtained from the waste heat of the light source device 4 becomes
in vain. Then, in the container portion 2, there may be provided a
heat insulation mechanism 10 by covering its circumference with
thermal insulating material, etc. for suppressing heat dissipation
so that the loss of the waste heat from the light source device 4
can be suppressed.
[0056] In this respect, that the water temperature providing a high
photocatalyst efficiency can be achieved and maintained by warming
the water with the waste heat of the light source device 4 and
providing the heat insulation mechanism 10 in the container portion
2 has been confirmed in the following simulation by the inventors
of the present embodiment. In the simulation, there was assumed a
structure, as in FIG. 1, that the light source device 4 generating
11.05 W of calorific power (the optical power 5 W, the
light-emitting efficiency 31.4%) was equipped in the container
portion 2 into which 500 ml of water had been poured (made of
glass, cylindrical, 40 mm in radius and 40 mm in height) while the
water from the container portion 2 was circulated in the heat
exchanger adjacent the light source device 4 through a tube (6 mm
in diameter, 1 m in length). Then, in this structure, the water
temperature rising rates (.degree. C./hr) at various water
temperatures when the water was assumed to be warmed with the waste
heat of the light source device 4 were computed under a normal
temperature (about 25.degree. C.) in the cases that the container
portion 2 was covered with and without thermal insulation material
(thermal conductivity 0.03 W/mK and 10 mm in thickness),
respectively. FIG. 6 shows the water temperature rising rate
(.degree. C./hr) at each water temperature. As illustrated, in the
case that the container portion 2 was not covered with thermal
insulation material, when the water temperature exceeded 45.degree.
C., the temperature fell (the water temperature rising rate was
negative) even in the warming of the water with the waste heat of
the light source device 4, and thus, the heat dissipating amount
exceeded beyond the heating amount of the water. On the other hand,
in the case that the container portion 2 was covered with thermal
insulation material, the water temperature rising rate was always
positive in the experimented temperature range, and thus, it was
confirmed that the condition that the water was warmed was
maintained. In particular, comparing with the result in FIG. 3B,
the water temperature did not fall in the above-mentioned structure
in the case that the water temperature was 50.degree. C. or more at
which a significant increase of the photocatalyst efficiency is
obtained. Accordingly, it has been shown that, by providing the
heat insulation mechanism 10 in the container portion 2, the water
can be warmed with the waste heat of the light source device 4, and
be effectively used in the production of hydrogen gas
[0057] Output Control of the Light Source Device
[0058] As already noted, in the hydrogen gas producing apparatus 1
of this embodiment, the electric power supplied to the light source
device 4 may be of renewable energy origin, such as obtained by a
solar panel 5. For the light irradiated on the photocatalyst, by
using the light emitted from the light source device with the
electric power converted from solar energy, instead of using the
sunlight directly, the wavelength of the light can be converted
into the wavelength band where the photocatalyst easily absorbs and
also the density of the light can be condensed, and thereby the
space occupied by the photocatalyst can be made small so that the
miniaturization of hydrogen gas producing apparatus will be
easy.
[0059] By the way, in a case of obtaining the light irradiated to
photocatalyst by supplying electric power to the light source
device 4 to make a light emitting element or a light-emitting
object emit the light, it has been found out that the light
emitting efficiency of a light emitting element or a light-emitting
object, such as LED, varies with the magnitude of the current
supplied thereto. According to the experiments of the inventors of
the present embodiment, when the light emitting efficiency (%) of
four LEDs, each exhibiting 1 A of the rated current and 3.54 V of
the rated voltage, connected in parallel, was measured, the light
emitting efficiency became its maximum under the condition that the
supplied current was a current (1.6 A) which was less than the
rated current (4 A) as illustrated in FIG. 7A. Namely, this shows
that, when the current, more than the current where the light
emitting efficiency is its maximum, is supplied to the light
emitting element or light-emitting object, the ratio of the energy
which is not converted into the light would increase relatively,
and thus the energy loss would increase. Then, in this embodiment,
it is preferable that the current supplied to the light source
device 4 is adjusted so that the light emitting efficiency of the
light emitting element or light-emitting object will be its
maximum. Or, in the current to be suppliable to the light source
device 4, the magnitude of the current in the light emitting
element or light-emitting object may be adjusted so as to make the
light emitting efficiency its maximum. Concretely, the light
emitting element or light-emitting object of normal power in which
the current giving the maximum light emitting efficiency flows when
the suppliable current is supplied to the light source device 4 may
be chosen. Thus, for instance, in a case that the electric power
source which supplies electric power to the light source device 4
is a solar panel, a light emitting element or a light-emitting
object may be preferably chosen so that the current which gives the
maximum light emitting efficiency will flow when the rated current
value of the solar panel is supplied.
[0060] Moreover, in a case that a power production source with
renewable energy, such as a solar panel, is used as an electric
power source which supplies electric power to the light source
device 4, the output of the power production source can be changed
with its environmental conditions, such as the sunshine condition,
and thus, the available current can vary every moment. In that
case, if the light source device is operated so that its light
emitting efficiency will be its maximum each moment, a good
efficiency of the energy used for production of hydrogen gas will
be obtained. As one way for this, in the light source device 4 of
this embodiment, there may be employed a structure that two or more
LEDs are connected in parallel for the light emitting elements or
light-emitting objects, as drawn in FIGS. 8A to 8C. In this
structure, the number of LEDs connected to the power production
source is adjusted in accordance with the output of the power
production source, and thereby, it is designed that, always,
currents giving the maximum light emitting efficiency flow in the
connected LEDs as much as possible. For instance, when the output
of the power production source is its normal power, all the LEDs
are connected to the power production source PV as shown in FIG. 8
(A), and when the output of the power production source is about a
half of its normal power, a half of the LEDs are connected to the
power production source PV as shown in FIG. 8B, and when the output
of the power production source is about 1/4 of its normal power as
shown in FIG. 8C, 1/4 of the LEDs is connected to the power
production source PV. Thereby, it becomes possible to achieve the
condition that the current giving the maximum light emitting
efficiency flows in each LED connected to the power production
source PV as illustrated in FIG. 7B. Namely, by adjusting the
number of LEDs connected in accordance with the output of the power
production source, the light emitting efficiency in each of LEDs
supplied with current from the power production source becomes as
close to its maximum as possible, so that the loss of the energy
which does not contribute to the generating of the light will be
suppressed.
[0061] Therefore, according to the hydrogen gas producing apparatus
1 of the present embodiment, in the structure of providing the
light irradiated to photocatalyst by a light source device which
operates with in the supply of electric power, the warming of the
water, which is the reactant, with the waste heat of the light
source device compensates the decrease in the production efficiency
of hydrogen gas due to the increase of the density of the light
irradiated to the photocatalyst from the light source device, and
thus, in the miniaturization of the apparatus by increasing the
amount of light irradiated to the photocatalyst per unit quantity,
the decrease in the production efficiency of hydrogen gas can be
suppressed, and thereby both the miniaturization and the increasing
of the efficiency of the apparatus are achieved. Furthermore,
according to the series of structures illustrated in FIG. 5,
through making the photocatalyst absorb as much light irradiated
from the light source device as possible and suppressing the loss
of the waste heat of the light source device as low as possible, it
becomes possible to make as much photon energy and thermal energy
from the light source device as possible contribute to the
production of hydrogen gas. Also, according to the structure as
illustrated in relation to FIGS. 7 and 8, by maximizing the light
emitting efficiency of the light source device as much as possible,
it becomes possible to make as much energy supplied to the light
source device as possible contribute to the production of hydrogen
gas. Thus, according to the series of structures of the present
embodiment, the further improvement of the energy efficiency in the
production of hydrogen gas is expected.
[0062] Although the above explanation has been described with
respect to embodiments of the present embodiment, it will be
apparent for those skilled in the art that various modifications
and changes are possible, and that the present embodiment is not
limited to the above-illustrated embodiments and may be applied to
various devices and apparatus without deviating from the concepts
of the present embodiment.
* * * * *